In general, microstripline filters in which striplines included in quarter-wavelength resonators are arranged so that open ends thereof are directed to a certain direction and the adjacent resonators are comb-line coupled with one another are used. In such a comb-line microstripline filter, a common electrode may be arranged so as to connect ends of a plurality of resonator lines on short-circuit sides with one another, and the resonators may be inductively coupled with one another (Refer to Patent Documents 1 and 2).
A microstripline filter according to Patent Document 1 includes a common electrode perpendicularly extending relative to striplines. First ends of all the striplines are commonly connected to the common electrode. Both ends of the common electrode are connected to a ground electrode in both surfaces which are parallel to the striplines.
FIG. 1 is a diagram illustrating an example of a configuration of a microstripline filter according to Patent Document 2. In a microstripline filter 101, striplines 102A to 102C are commonly connected to a common electrode 103 at first ends thereof. Furthermore, the common electrode 103 is connected to a short-circuit electrode 104. The short-circuit electrode 104 extends in parallel to the striplines 102A to 102C and is grounded in a ground electrode 105.    [Patent Document 1] Japanese Unexamined Utility Model Application Publication No. 56-105902    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-270508